Communication devices such as wireless devices are also known as e.g. user equipments (UE), mobile terminals, wireless terminals, and/or mobile stations. Wireless devices are enabled to communicate wirelessly in a cellular communications network or wireless communication system, sometimes also referred to as a cellular radio system or cellular networks. The communication may be performed e.g. between two wireless devices, between a wireless device and a regular telephone and/or between a wireless device and a server via a Radio Access Network (RAN) and possibly one or more core networks, comprised within the cellular communications network.
Wireless devices may further be referred to as mobile telephones, cellular telephones, laptops, tablet computers or surf plates with wireless capability, just to mention some further examples. The wireless devices in the present context may be, for example, portable, pocket-storable, hand-held, computer-comprised, or vehicle-mounted mobile devices, enabled to communicate voice and/or data, via the RAN, with another entity, such as another wireless device or a server.
The cellular communications network covers a geographical area which is divided into cell areas, wherein each cell area being served by a radio network node. A cell is the geographical area where radio coverage is provided by the radio network node.
The radio network node may e.g. be a base station such as a Radio Base Station (RBS), eNB, eNodeB, NodeB, B node, or Base Transceiver Station (BTS), depending on the technology and terminology used. The base stations may be of different classes such as e.g. macro eNodeB, home eNodeB or pico base station, based on transmission power and thereby also cell size.
Further, each radio network node may support one or several communication technologies. The radio network nodes communicate over the air interface operating on radio frequencies with the wireless terminals within range of the radio network node. In the context of this disclosure, the expression Downlink (DL) is used for the transmission path from the base station to the mobile station. The expression Uplink (UL) is used for the transmission path in the opposite direction i.e. from the mobile station to the base station.
In 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE), base stations, which may be referred to as eNodeBs or even eNBs, may be directly connected to one or more core networks.
Discontinuous Reception (DRX) is a known technique in telecommunications for reducing the power consumption of a UE such as a mobile terminal or a Machine-Type-Communication (MTC) device. A UE may have two Radio Resource Control (RRC) states, an RRC_CONNECTED state and an RRC_IDLE state. When the DRX functionality is configured, a UE is allowed to monitor a downlink control channel discontinuously. During each DRX cycle, a UE wakes up at least once to monitor the downlink control channel. DRX cycles of different lengths are defined, for example, a DRX long cycle, a DRX short cycle, and an idle_mode DRX cycle. A UE often supports DRX long and short cycles when in an RRC_CONNECTED state, and a UE often supports idle_mode DRX cycles when in an RRC_IDLE state.
Separate mobility schemes are defined for the RRC_IDLE state and the RRC_CONNECTED states respectively, see also the 3GPP Technical Specification (TS) 36.300, Release 11, Section 10. When a UE is in an RRC_CONNECTED state, the mobility scheme is referred to as a network-controlled mobility scheme, which is based on network-controlled UE-assisted handovers. The network-controlled mobility scheme supports the currently specified DRX long cycles ranging from 10 ms to 2560ms. When a UE in RRC_CONNECTED state needs to communicate with a network, such as with a network node comprised in the network, the network will schedule the UE on the Physical Downlink Control Channel (PDCCH) for an Uplink (UL) grant, a Downlink (DL) assignment, or ordering the UE to perform a Random Access.
When a UE is in an RRC_IDLE state, the mobility scheme is referred to as a terminal-controlled mobility scheme, which is based on cell reselections. The terminal-controlled mobility scheme supports the currently specified idle_mode DRX cycles ranging from 320 ms to 2560 ms. When the network needs to reach a UE that is in RRC_IDLE state, the network will page the UE at specific times on the PDCCH when the UE is scheduled to tune in to that channel for paging messages. Paging is used for network-initiated connection setup when the UE is in an RRC_IDLE state.
Both mobility schemes require periodic measurements to be performed. In RRC_IDLE, DRX usage is assumed and all requirements are related to the idle mode DRX cycle. In RRC_CONNECTED, both DRX usage and non-DRX usage are supported. Radio Resource Management (RRM) requirements are different for DRX usage and non-DRX usage, respectively. As an example, RRM requirements may relate to how often the measurements should be performed. In practice, when a UE or a MTC type device supports DRX, the measurement times are scaled with the DRX long cycles so that it is possible to perform measurements only when the device is in DRX active state, i.e. awake. Furthermore, a more complete definition on when the non-DRX requirement is applied, is formulated based on which DRX timers are running, and what recent events have happened. See 3GPP TS 36.133, Release 11, Section 5.
However, when DRX long cycles are further extended for MTC type traffic, current implementations may be incompatible with the measurement times, when the measurement times are being scaled with the DRX long cycles. The scaled measurement times may cause Radio Link Failures (RLFs) or increased signaling between a UE and a network node during handover. Furthermore, the frequent signaling required by current implementations may result in high UE battery usage.